Which Air Circulation Mode to Use When the Car Fogs Up in Summer?

[DelMaggie]

In summer, when the car fogs up, turn on the external air circulation and cold air. During summer driving, drivers usually turn on the air conditioning to combat the hot weather. Over time, due to the significant temperature difference between the inside and outside, the windows may fog up to varying degrees. At this point, it is necessary to switch to external air circulation. Low temperatures can damage the compressor of the air conditioning system. Under normal summer conditions, the air conditioning temperature should ideally be set between 24°C and 27°C. Car air conditioning refers to the air conditioning device installed in vehicles, which serves the following purposes: 1. Cooling, heating, ventilating, and purifying the air inside the cabin; 2. Providing a comfortable environment for passengers, reducing driver fatigue, and enhancing driving safety.

[OIsaac]

I've been driving for over a decade, and fogging up in summer is quite common. Window fogging mainly occurs due to significant temperature differences between inside and outside the car combined with high humidity. The correct approach is to turn on the air conditioning for cooling, then press the external circulation button. External circulation draws in dry air, which works with the AC's dehumidification function to quickly clear the fog. Remember not to use internal circulation, as it traps moisture inside and can worsen fogging. I usually switch back to auto mode after defogging. If fog keeps reappearing while driving, it might be time to change the AC filter – a dirty one can reduce dehumidification effectiveness.

[LeAndres]

Last month, while driving with my family on a trip, we encountered heavy rain and the car windows fogged up. I immediately turned on the air conditioning, pressed the defog button (the one with the fan-shaped icon), and switched the circulation mode to external air. The cold air combined with the fresh air from the external circulation cleared the fog in just half a minute. Later, I asked a car repair friend and learned that using internal circulation in summer is like holding your breath in a steamer—the moisture can't escape. It's recommended to aim the air vents at the windshield, increase the fan speed, and lower the temperature for better results. Also, during the rainy season, it's best to check the wipers in advance, as leftover cleaning residue can worsen fogging.

[BryceRose]

As a car enthusiast, I've studied the principles of air conditioning systems. In summer, you should turn on the external air circulation when defogging because the outside air gets dehumidified when passing through the AC evaporator. Dry air blown onto the windshield can quickly eliminate fog. If you use internal circulation, it's equivalent to letting humid air recirculate inside the car. My car has dual-zone climate control, and practical tests show that synchronizing the passenger side with external circulation achieves more even defogging. Also, don't rush to turn off the AC - continuous cooling and dehumidification prevent repeated fogging. Some cars come with humidity sensors that automatically switch between internal and external circulation, which is particularly convenient.

[CalebRose]

Last week, while driving to pick up my girlfriend, I encountered annoying fogging. Turning on the AC and selecting the external air circulation worked immediately. The principle is quite simple: the moisture from passengers' breath condenses on the cold glass. External circulation is like opening a window for ventilation, but it's quieter and more fuel-efficient than actually opening the window. Avoid using internal circulation, as it stirs up moisture from the floor mats and seats. A small detail: don’t panic if you see white mist when you first turn on the AC—it’s just the refrigerant meeting hot air, a normal phenomenon. If the fogging is really heavy, it’s best to pull over and wipe the windows—safety first.

[ElainaLee]

I commute two hours every day and have encountered fogging issues multiple times when using the air conditioning in summer. The correct approach is to turn on the AC cooling + external air circulation, with the temperature set around 22°C for optimal results. This is because external circulation draws in drier air from outside (summer outdoor humidity is usually lower), which, combined with the dehumidifying effect of the AC, is much safer than wiping with a cloth. Remember to maintain the AC system regularly, especially by cleaning the condenser and replacing the filter, as older cars may experience slower defogging due to insufficient cooling. If you notice repeated fogging during long-distance driving, it might be due to aging door seals allowing external moisture to seep in—time for an inspection.